Simple interest is money you earn on savings, or pay on a loan, based only on the starting amount. Use the formula . Multiply the principal by the yearly interest rate , written as a decimal, and the time in years. For example, $500 at 4% for 3 years earns , or $60. Before this…
Percent word problems use percents to find real prices. For a discount, find the percent of the price and subtract it. For sales tax, a tip or a markup, find the percent and add it. For example, a $40 shirt that is 25% off costs 40 − 10 = $30, because 25% of 40 is…
Percent change tells how much an amount went up or down, compared to where it started. Subtract to find the change, divide by the original amount, then multiply by 100. If a price goes from $50 to $60, the change is $10, and 10 ÷ 50 = 0.20. That is a 20% increase. Before this…
Unit conversions change a measurement from one unit to another, like feet to inches or minutes to hours. Multiply by a conversion factor, which is a fraction equal to 1, such as . Put the unit you want on top, so the old unit cancels. For example, . Before this lesson: You should know how…
A unit rate tells how much of one thing there is for exactly 1 unit of another, like 60 miles per hour or $3 per pound. To find a unit rate, divide the first amount by the second amount. For example, $12 for 4 pounds of apples is 12 ÷ 4 = $3 per pound….
A ratio compares two amounts. If a shelter has 3 cats and 5 dogs, the ratio of cats to dogs is 3 to 5. You can write it as 3 to 5, 3:5 or . Equivalent ratios make the same comparison, like 3:5 and 6:10. To find equivalent ratios, multiply or divide both numbers by…
Converting fractions and decimals works in both directions. To change a fraction to a decimal, divide the top by the bottom: . To change a decimal to a fraction, write its digits over 10, 100 or 1,000 and simplify: . Some fractions never end, like Before this lesson: You should know how to simplify fractions…
Mixed numbers and improper fractions are two ways to write an amount bigger than 1. A mixed number has a whole number and a fraction, like . An improper fraction has a top number that is at least as big as the bottom, like . To change , multiply 2 by 4 and add 3…
Multiplying and dividing fractions is often easier than adding them. To multiply, multiply the numerators and multiply the denominators. To divide, flip the second fraction and multiply. For example, and . When you are done, simplify the answer if the top and bottom share a factor. Before this lesson: You should know how to simplify…
Adding and subtracting fractions is easy when the denominators match: add or subtract the numerators and keep the denominator. If the denominators are different, first rewrite the fractions with a common denominator. For example, . Then simplify the answer if you can. Before this lesson: You should know how to write equivalent fractions and how…
